Rechargeable lithium-ion and lithium-polymer batteries are used widely for portable electronics like cell phone and earphones. For extremely small applications like hearing aids, volumetric energy density is the key consideration. In U.S. patent application Ser. No. 12/881,179 published on Apr. 21, 2011 Pub. No. US 2011/0091753A1 by Wang et al. a novel button cell configuration with spiral wound electrodes was provided which has great advantages on volumetric energy density over lithium-polymer battery or stacked electrodes button cell. Detailed comparisons of different prior arts were described in that patent.
In U.S. patent application Ser. No. 12/881,179 the electrodes are tapered in width to adapt to the height changes in the battery inner casing which leaves a shoulder for the outer casing and insulation gasket to be crimped on to form a reliable sealing. The electrodes comprise current collectors of metal foils coated with lithium-intercalating active materials, leaving small area of uncoated metal foils as conductor tabs for connecting to the casings. The tabs are welded to the casings respectively, or for the tab of the electrode which connecting to outer casing, welded to an aluminum flake first and said flake is pressed on the outer casing by said gasket.
The tab connecting to the outer casing will need to be welded to a metal flake first, or, by extending its length, to be welded directly to the flat inner surface of the outer casing. Both methods need much care and as the tab comprising copper or aluminum foil is very thin, usually the thickness is just 0.006 mm to 0.016 mm, most probably at 0.012 mm of aluminum, they are easy to be broken during the welding process and/or cell assembly steps hence the cell would fail.
In above patent the insulation washers are also used to cover the inner surface of the casings to prevent battery short. However, as the tab connecting to the outer casing is in a complicated way, so to fully cover the metal flake by one washer is difficult. Exposing to the electrolyte of the naked metal on the cathode casing or naked metal connected to the cathode casing—usually the outer casing—is found to be one of the causes for battery short and/or shorter cycle life.
In U.S. patent application Ser. No. 13/378,117 published on Apr. 26, 2012 Pub. No. US 2012/0100406A1 by Gaugler, spiral wound electrodes were also used but without taper on width. It has no mechanical crimping to seal the battery just press the outer casing horizontally on the gasket and inner casing. Such design does not have closing force on the vertical direction of the cell. The electrodes are firstly welded with conductors and then the conductors are welded to the casings by laser from the outside of the cell, after the cell is closed. It is a bold design while the reliability of such configuration is in question.
Therefore, it is the object of the present invention to provide an easier and reliable connecting method for the electrodes to be connected to the battery casings.
It is another object of the present invention to provide a better method to prevent the cell from short circuit, covering all the naked metals at cathode tab and cathode casing not to be exposed to electrolyte, hence the battery will have high reliability and longer cycle life.